Remove PNaCl QUnicodeTables workaround.

The bug is no longer present on current versions of
the toolchain (tested: pepper_42). This was also causing
QChar::toLower() and QML compilation errors.

Change-Id: I9fda442d9ec954ceaa5bf63312bcc1d656e2e543
Task-number: QTBUG-50302
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>